[TIL/05.07] Leetcode: Group Anagrams (Python)

문제

A phrase is a palindrome if, after converting all uppercase letters into lowercase letters and removing all non-alphanumeric characters, it reads the same forward and backward. Alphanumeric characters include letters and numbers.

Given a string s, return true if it is a palindrome, or false otherwise.

 

Example 1:

Input: s = "A man, a plan, a canal: Panama"
Output: true
Explanation: "amanaplanacanalpanama" is a palindrome.

Example 2:

Input: s = "race a car"
Output: false
Explanation: "raceacar" is not a palindrome.

Example 3:

Input: s = " "
Output: true
Explanation: s is an empty string "" after removing non-alphanumeric characters.
Since an empty string reads the same forward and backward, it is a palindrome.

 

Constraints:

• 1 <= s.length <= 2 * 105
• s consists only of printable ASCII characters.

내 풀이

class Solution:
    def isPalindrome(self, s: str) -> bool:
        s2 = ""
        # 1. toLower
        s = s.lower()

        # 2. remove non-alphanumeric characters
        for ch in s:
            if (ch.isdigit() or 
            (ord('A') <= ord(ch) <= ord('Z')) or (ord('a') <= ord(ch) <= ord('z'))):
                # add to new string 
                s2 += ch

        # 3. judge if it's a palindrome
        if s2[::-1] == s2:
            return True

        return False

 

해설 풀이

class Solution:
    def isPalindrome(self, s: str) -> bool:
        l = 0
        r = len(s) - 1

        while l < r:
            while l < r and not self.alphaNum(s[l]):
                l += 1  
            while r < l and not self.alphaNum(s[r]):
                r -= 1
            if s[l].lower() != s[r].lower():
                return False

            l, r = l+1, r-1 

        return True
    
    def alphaNum(self, c):
        return (ord('A') <= ord(c) <= ord('Z') or
        ord('a') <= ord(c) <= ord('z') or
        ord('0') <= ord(c) <= ord('9'))

 

➤ two pointer 기법 사용

 

배운 내용

🔑 문제 풀기 전 알아둬야 할 것!

Non-alphanumeric characters refer to those characters that are neither alphabets (a-z) nor numbers(0-9)

 

🚫 오류 기록

invalid literal for int() with base 10: 'a' Error

➤ ord(ch)가 실패한 이유는 현재 문자 ch가 알파벳이나 숫자가 아닌 경우에는 해당 문자를 정수로 변환할 수 없기 때문

 

 

✏️ 배움 기록

문자열인지 숫자인지 판단

1. 숫자판별 - isdigit()

s = "28212"
print(s.isdigit())	# True

# contains alphabets and spaces
s = "Mo3 nicaG el l22er"
print(s.isdigit())	# False

 

2. 문자열 판별 - isalpha()

name = "Monica"
print(name.isalpha())	# True

 

3. 숫자 + 문자열 판별 isalnum( )

name = "M234onica"
print(name.isalnum())	# True